Basionym (or base-name) is a taxonomic term used in botany to refer to a previously valid binomial name of a species that has since been renamed and from which the new name is partially derived.
The basionym of Picea abies (the Norway Spruce), for example, is Pinus abies. Although the species was originally called Pinus abies by Carolus Linnaeus, botanist Karsten later transferred it to the genus Picea.
The term basionym is defined by the International Code of Botanical Nomenclature as a "name-bringing or epithet-bringing synonym".1 Consequently, for an earlier name to be described as a basionym the new name must retain some part of the earlier name, although not necessarily in its entirety. For example the gender may change as with Acrocarpia paniculata, the basionym of which is Fucus paniculatus. Where an entirely new name (nomen novum) is created the term basionym is not used.1
Most commonly, a species will be renamed because it is discovered to be either more or less closely related to another species than was previously realized. As the first part of a binomial name is the genus, if the genus changes then the binomial name also needs to change. The second part of the species name, known as the epithet, is specific to the species however and can therefore be retained.
Bacteriology uses a similar term, basonym, spelled without an i,2 while the concept is not formally used in zoology.
